1. Field of the Invention
The present invention relates to torque wrenches, and more particularly, to a to a torque wrench with functional lock.
2. Description of the Related Art
A conventional wrench is known comprising a hollow main shaft, a tool member mounted at one end of the hollow main shaft for driving a screw nut or screw bolt, and an adjustable grip rotatably mounted at an opposite end of the hollow main shaft, and a clutch device and a spring member mounted inside the hollow main shaft and set between the tool member and the adjustable grip. The adjustable grip can be rotated to push the spring member, thereby changing the prestress of the spring member. The clutch device can be disengaged when the tool member receives a torque larger than the elastic prestress of the spring member, thereby limiting the torque acted on the tool member. Further, during clutch action of the clutch device, an escape percussion sound will be produced to notice the user of the problem that the applied force has been over the limit, avoiding screw nut or screw bolt damage.
U.S. Pat. No. 5,129,293 discloses a torque wrench tool 10, comprising a drive head 11 disposed in one end of a housing 17. The other end of the housing 17 is provided with a handle 22, while a lock ring retainer 20 is disposed between the handle 22 and the housing 17, wherein the lock ring retainer 20 is fastened to the periphery of a thimble 19 through a handle lock screw 21a. When torque value of the tool 10 is being adjusted, the handle lock screw 21a has to be unscrewed by a screwdriver, whereby the handle is allowed to be driven to rotate for adjusting. Such method of adjustment is inconvenient; in addition, when the user forgets to screw up the handle lock screw 21a, the wrench loosens easily, causing an incorrect torque value.
Also, U.S. Pat. No. 6,948,410 discloses another torque wrench 10, comprising a body 20 with a head 30 on one end and a handle 40 on the other end. A locking sleeve 50 is disposed between the handle 40 and the body 20, while the locking sleeve 50 is able to move between a locked position and an unlocked position along an axis A. Therein, as shown by FIG. 3, when the locking sleeve 50 is in the locked position, an annular wall 54 of a generally cylindrical rigid member 52 keeps a locking ball 60 radially inward and placed in a flute 28 axially positioned on the body 20, thereby limiting the rotation of the handle 40. As shown in FIG. 4 and FIG. 5, when the locking sleeve 50 is in the unlocked position, the handle 40 is allowed to rotate against the body 20, whereby the locking ball 60 is able to radially move and detach from the flute 28 for pressing an O-ring 58. Therefore, the handle 40 is allowed to be rotate in clockwise or counter clockwise against the body 20 for adjusting the torque. However, during the process of switching, the locking sleeve 50 is stopped against the locking ball 60 through the O-ring 58, so that the hand feeling during the position switching process between the locked position and the unlocked position is not obvious. As a result, the user may not notice that the wrench is not adjusted to the proper position, causing the inconvenience. At the same time, after being used for a period of time, the O-ring 58 tends to be deformed or damaged due to the environmental conditions.